Current dry low NOx combustion systems require tuning to achieve correct combustor temperatures. This is achieved in some instances by means of air dilution holes provided in the transition piece extending between the turbine and the first combustor stage. The air flowing through the holes serves as bypass and dilution air, but occasionally needs to be adjusted after turbine commissioning in the field. The current designs utilizing simple dilution holes require a lengthy and costly down time so that the transition pieces can be removed and resized. Specifically, the transition pieces must be stripped of their thermal barrier coating, patch welded, machined to add new holes, heat treated and recoated with the thermal barrier coating. In U.S. Pat. No. 6,499,993, owned by the assignee of this invention, there is provided a mechanical arrangement enabling external access to the combustion chamber which facilitates changeover of combustor dilution-hole areas to adjust the NOx levels without disassembly of the combustors. More specifically, the assembly is provided with a boss, an orifice plate, and a retaining ring. The retaining ring is tapered, and in cooperation with a matching taper in the ring grooves, provide a wedging method for holding the orifice plate tightly in place. The boss design does not, however, have a flexible-weld distortion tolerant feature, which can lead to distortion of the undesirable distortion in the boss hole and orifice plate dimensions.